1. Field of the Invention
The present invention relates to a paper feed control system in a printer such as a typewriter and, more particularly, to a paper feed control system which compensates for a feed error caused by the backlash of the transmission gear mechanism.
2. Description of the Prior Art
A paper feed system in a printer, especially a typewriter, generally includes a platen for supporting a recording paper sheet. The platen is mechanically connected to a paper feed drive motor such as a pulse motor via a transmission gear mechanism. The platen is rotated by the paper feed drive motor so that the recording paper sheet mounted on the platen is fed forward or backward (reverse) so as to position the recording paper sheet at a desired location.
In such a paper feed system, accurate paper placement is difficult to control due to backlash in the transmission gear mechanism which is disposed between the platen and the paper feed drive motor, or due to looseness included in the bearing portion of the transmission gear mechanism.
The backlash greatly influences the accuracy of the paper sheet placement if the printing operation is conducted after a certain amount of forward feed, and then the printing operation is carried out subsequent to a certain amount of reverse feed. Therefore, in the conventional system, when the reverse feed is conducted, the reverse feed is first conducted to a predetermined amount which is greater than a desired amount by an excess distance corresponding to several pulses, and then, the forward feed is carried out by the excess distance so as to minimize the positioning error caused by the backlash.
However, as is well known, the paper feed can be manually conducted in addition to the motor driven automatic feed. In the manual feed operation, the platen is manually rotated to shift the recording paper sheet around the platen. In the conventional system, the positioning error caused by the backlash can not be compensated for when the manual feed is conducted between sequential two operations of the motor driven automatic feed. More specifically, when the motor driven automatic feed is conducted after the manual forward feed or the manual reverse feed, the motor driven automatic feed is carried out from a position which includes the backlash error created in the manual feed operation.